A well-known gas engine is started by a self-starter or a recoil starter. As for some gas engine started by a self-starter, a battery for the self-starter is provided for actuating a solenoid valve to allow quick supply of a gas fuel for improving startability of the gas engine. Use of a solenoid valve to allow quick supply of a gas fuel for successfully starting a gas engine is disclosed in, for example, JP-A-7-103006.
JP-A-7-103006 discloses a fuel supply system is provided for quickly supplying a gas fuel to a gas engine. However, this system has a complex structure because the system includes a battery, a self-starter and a solenoid valve, and a control unit for controlling the solenoid valve. Such a complex structure has a high cost and a heavy weight.
A gas engine provided with a recoil starter is started by manually pulling the recoil starter. Thus, a fuel supply system for such a gas engine provided with the recoil starter need not include a self-starter or battery for starting the gas engine. However, the fuel supply system for the gas engine provided with the recoil starter cannot quickly supply a gas fuel to the gas engine by using a solenoid valve as disclosed in JP-A-7-103006.
To address problems regarding the quick supply of the gas fuel, it is well-known in the art that an intake flow passage for introducing a gas fuel into a combustion chamber of a gas engine is provided with a choke valve. This choke valve is designed to be closed to create a high vacuum in the intake flow passage for opening a fuel shut-off valve to allow quick supply of a gas fuel.
A natural gas used as a gas fuel has a narrower flammable range suitable for starting a gas engine than LP Gas or gasoline. It may be troublesome to control the choke valve to precisely control the fuel shut-off valve in correspondence to the narrow flammable range of the natural gas.